Observational Cosmology (C. Porciani / K. Basu) Lecture 4 The - PowerPoint PPT Presentation

Observational Cosmology (C. Porciani / K. Basu) Lecture 4 The Cosmic Microwave Background (Secondary Anisotropies & Polarization) Course website: http://www.astro.uni-bonn.de/~kbasu/astro845.html Observational Cosmology Lecture 3 (K. Basu): CMB spectrum and anisotropies

Outline of today’s lecture CMB secondary anisotropies Polarization signal of the CMB Observation of the CMB: receivers, telescopes 2 Observational Cosmology Lecture 3 (K. Basu): CMB spectrum and anisotropies

Questions? 3 Observational Cosmology Lecture 3 (K. Basu): CMB spectrum and anisotropies

Recap: Temperature anisotropies • angular scale Three acoustic peak observables: • photon-to-baryon ratio • radiation-to-matter ratio (plus information about the shape of initial matter power spectrum) 4 Observational Cosmology Lecture 3 (K. Basu): CMB spectrum and anisotropies

Recap: Dependance on parameters 5 Observational Cosmology Lecture 3 (K. Basu): CMB spectrum and anisotropies

Summary of temperature anisotropies 6 Observational Cosmology Lecture 3 (K. Basu): CMB spectrum and anisotropies

Integrated Sachs-Wolfe e fg ect • The early ISW e fg ect is caused by the small but non-negligible contribution of photons to the density of the universe • The late ISW e fg ect • Gravitational blueshift on infall does not cancel redshift on climb-out • Contraction of spatial metric doubles the e fg ect: Δ T/T ~ 2 ΔΦ • E fg ect of potential hills and wells cancel out on small scales 7 Observational Cosmology Lecture 3 (K. Basu): CMB spectrum and anisotropies

ISW e fg ect as Dark Energy probe The ISW e fg ect constraints the dynamics of acceleration Cosmic evolution of dark energy is parametrized by w(a) ≡ p DE / ρ DE for cosmological constant, w=-1. In general, ρ DE ~ a -3(1+w) 8 Observational Cosmology Lecture 3 (K. Basu): CMB spectrum and anisotropies

Cosmic variance problem Power spectrum sampling error = [(l+1/2) f sky ] -1/2 Low multipole signals are severely cosmic variance limited Solution : Cross-correlate with other probes of dark energy, with large sky coverage (optical, X-ray or radio surveys) Corasaniti, Giannantonio, Melchiorri 2005 9 Observational Cosmology Lecture 3 (K. Basu): CMB spectrum and anisotropies

Non-linear e fg ects of gravity Once non-linear structures like clusters form, linear perturbation theory approximation breaks down. Cancellation of the ISW e fg ect on small scales leaves second order and non-linear analogues in its wake. From a single isolated structure, the potential along the line of sight can change not only from evolution in the density profile but more importantly from its bulk motion across the line of sight. In the context of clusters of galaxies, this is called the moving cluster e fg ect 10 Observational Cosmology Lecture 3 (K. Basu): CMB spectrum and anisotropies

Δ T from reionization Re-scattering of CMB photons damps anisotropy power as e -2 τ , with τ the optical depth to Thomson scattering New perturbations are generated on small scales due to the bulk motion of electrons in over-dense regions (Ostriker-Vishniac e fg ect) 11 Observational Cosmology Lecture 3 (K. Basu): CMB spectrum and anisotropies

Local reionization: SZ e fg ect 12 Observational Cosmology Lecture 3 (K. Basu): CMB spectrum and anisotropies

SZ power spectrum SZ power spectrum is a powerful probe of cosmology, primarily through its strong dependance on σ 8 Text 13 Observational Cosmology Lecture 3 (K. Basu): CMB spectrum and anisotropies

Power at small angular scales Please note that, the signal is actually C l ! Our power spectrum plots boosts the apparent variance at large l by a factor l 2 ! Observations at high- l therefore requires far greater sensitivity. 14 Observational Cosmology Lecture 3 (K. Basu): CMB spectrum and anisotropies

Polarization of the CMB 15 Observational Cosmology Lecture 3 (K. Basu): CMB spectrum and anisotropies

What makes CMB polarized? Two things: “Normal” CDM: Density perturbations at z=1100 lead to velocities that create local quadrupoles seen by scattering electrons. => “E-mode polarization” (no curl) Gravity waves: create local quadrupoles seen by scattering electrons. => “B-mode polarization” (curl) 16 Observational Cosmology Lecture 3 (K. Basu): CMB spectrum and anisotropies

Quadrupole + Thomson scattering Polarization is induced by Thomson scattering, either at decoupling or during a later epoch of reionization. (No circular polarization, i.e. V=0) 17 Observational Cosmology Lecture 3 (K. Basu): CMB spectrum and anisotropies

E and B modes Two flavors of CMB polarization: Density perturbations: curl-free, “E-mode” • We can break down the polarization Gravity waves: curl, “B-mode” field into two components which we call E and B modes. This is the spin-2 analog of the gradient/curl decomposition of a vector field. E-mode • E modes are generated by density (scalar) perturbations via Thomson scattering. • B modes are generated by gravity waves (tensor perturbations) at last scattering or by gravitational B-mode lensing (which transforms E modes into B modes along the line of sight to us) later on. 18 Observational Cosmology Lecture 3 (K. Basu): CMB spectrum and anisotropies

Polarization pattern The scaler quadrupole moment, l=2, m=0. Note the azimuthal symmetry in the transformation of this quadrupole anisotropy into linear polarization. 19 Observational Cosmology Lecture 3 (K. Basu): CMB spectrum and anisotropies

Parity of E & B modes 20 Observational Cosmology Lecture 3 (K. Basu): CMB spectrum and anisotropies

Polarization power spectra E & B modes have di fg erent reflection TT properties (“parities”): Tensors EE TE Parity: (-1) l for E and (-1) l +1 for B BB for r=0.5 Lensing The cross-correlation between BB for r=10 -4 B and E or B and T vanishes (unless there are parity- violating interactions), because B has opposite parity to T or E. r = T/S: primordial gravity waves We are therefore left with 4 (tensor modes) fundamental observables. 21 Observational Cosmology Lecture 3 (K. Basu): CMB spectrum and anisotropies

Shape of the power spectra • The primordial B-mode signal reionization (due to a stochastic bump background of gravitational waves) dominates only at intermediate angular scales • On very large scales, the polarization signal is dominated by secondary fluctuations imprinted by reionization • The lens-generated signal grows at smaller scales Shape and amplitude of EE are predicted by Λ CDM. Shape of BB is predicted “scale-invariant gravity waves”. Amplitude of BB is model dependent, and not really constrained from theory. Measuring this amplitude would provide a direct handle of the energy scale of inflation! 22 Observational Cosmology Lecture 3 (K. Basu): CMB spectrum and anisotropies

EE power spectrum MCMC simulations from K. Vanderlinde • Most parameters already well measured from TT. • EE spectrum is a fundamental check on our understanding. • EE is also sensitive to nonstandard model e fg ects (e.g. isocurvature) 23 Observational Cosmology Lecture 3 (K. Basu): CMB spectrum and anisotropies

BB spectrum uncertainties MCMC simulations from K. Vanderlinde Lensing Tensors BB mode can tell us about a lot of new physics (energy scale at inflation, neutrino mass, etc.), but its prediction is still very uncertain. Current data only puts the limit r = T/S < 0.2 24 Observational Cosmology Lecture 3 (K. Basu): CMB spectrum and anisotropies

Polarization simulations Seljak and Zaldarriaga, astro-ph/9805010 Bars: polarization direction and size 25 Observational Cosmology Lecture 3 (K. Basu): CMB spectrum and anisotropies

Detection of polarization • The DASI experiment at the South Pole was the first to detect E-mode CMB polarization • It was followed by WMAP’s measurement of C TE (l) for l<500 • Both the BOOMERANG and the CBI experiments have reported measurements of C TT , C TE , C EE and a non-detection of B modes • E-mode has also been measured by CAPMAP and Maxipol • B-mode polarization has not been DASI collaboration, 2002 detected yet (current noise level is 50 K at the arcmin scale, future ground- based experiment will go down to 5 K) 26 Observational Cosmology Lecture 3 (K. Basu): CMB spectrum and anisotropies

Polarization state-of-the-art Measurement of the TE correlation Constraints on the EE power 27 Observational Cosmology Lecture 3 (K. Basu): CMB spectrum and anisotropies

WMAP measurement Re-scattering of the CMB photons during and after reionization added to the polarized power on large angular scales (scale comparable to the horizon, H -1 , at the epoch of scattering) 28 Observational Cosmology Lecture 3 (K. Basu): CMB spectrum and anisotropies

Planck: polarization sensitivity 29 Observational Cosmology Lecture 3 (K. Basu): CMB spectrum and anisotropies

Polarized foregrounds (CMB Task Force Report) RMS fluctuations in the polarized CMB and foreground signals as function of frequency 30 Observational Cosmology Lecture 3 (K. Basu): CMB spectrum and anisotropies